1. Field of Application
The present invention relates to a synchronous AC motor, suitable for installation in a motor vehicle, and to a control apparatus for the AC motor.
2. Description of Prior Art
In the prior art, types of synchronous AC motor, and in particular types of brushless AC motor, are known which have stator windings formed as closely packed layers of conductors that are wound around the stator poles, for example as described in Japanese Patent Laid-open No. 6-261513 (page 3, and FIGS. 1 to 3), designated in the following as reference document 1. FIGS. 40 and 41 are cross-sectional views taken along the motor shaft and at right angles to the motor shaft, respectively, showing the general configuration of such a prior art type of brushless motor. This example is a 4-pole 6-slot type of brushless motor, having compensating windings formed on the stator, and with respective stator windings of the phases (referred to in the following simply as the phase windings) being wound around the stator poles. FIG. 42 is a conceptual view taken around 360° of the inner circumference of the stator (with such a type of view being referred to in the following as a developed circumferential view), illustrating how the stator windings are disposed with respect to the corresponding stator poles. The extent of the (mechanical) 360° developed circumferential view of FIG. 42 is equivalent to an electrical angle of 720°. The rotor 2 of this brushless motor is formed with two permanent magnets designated by numeral 7 which have N (north) polarity at the outer surface of the rotor 2, as the N poles of the rotor 2, and two permanent magnets designated by numeral 8 which have S (south) polarity at the outer surface of the rotor 2, as the S poles of the rotor 2, with the N poles 7 and S poles 8 being arranged in successive alternation around the circumferential periphery of the rotor 2 as shown. The stator 4 has U-phase stator poles TBU1 and TBU1 having the U-phase stator windings WBU1, WBU2 respectively wound thereon, and similarly has V-phase stator poles TBV1 and TBV1 having the V-phase stator windings WBV1, WBV2 respectively wound thereon, and has W-phase stator poles TBW1 and TBW1 having the W-phase stator windings WBW1, WBW2 respectively wound thereon.
Such a configuration of brushless motor is widely used at the present time in both industrial and domestic applications. However such a brushless motor has a complex construction, due to the need to form windings around each of the respective stator poles, with each of the windings being disposed in the interior of a stator slot. Hence, the manufacturing productivity is low.
In addition, it is difficult to produce such a type of brushless motor in a compact size, or to manufacture it at low cost.
It should be noted that although the present invention is described in the following with reference to a brushless type of synchronous AC motor in which rotor poles are formed by permanent magnets, or to a reluctance type of synchronous AC motor, the principles of the invention are equally applicable to a synchronous AC motor having field windings that are driven by an excitation current to produce the magnetic flux for the rotor poles.